Necrotizing enterocolitis (NEC) is a life-threatening inflammatory bowel disorder of unknown cause that affects approximately 10% of premature infants born <1500gm. Prematurity is the greatest risk factor rather than any particular insult, suggesting that intestinal immaturity is a fundamental issue. However, the exact aspects of immaturity contributing to NEC are poorly understood. I have found that a key point of developmental difference between immature and mature intestinal epithelial cells (IEC) is regulation of nuclear factor kappaB. In response to RFA-HD-07-08 New Approaches for the prevention and treatment of necrotizing enterocolitis, I propose to test the hypothesis that an intrinsic immaturity of intestinal epithelial cell NF-kB regulation leads to an exaggerated inflammatory response predisposing the preterm infant to NEC. Furthermore I hypothesize that soluble factors secreted by probiotic bacteria can modulate NF-kB regulation and preserve intestinal barrier function, thus decreasing inflammation and protecting against NEC. Preliminary data for this proposal demonstrate that compared to mature IEC, immature IEC have differences in regulation of both inhibitory kappaB alpha and A20 - key NF-kB down-regulatory proteins. Furthermore, our preliminary data demonstrate that secreted products from probiotic bacteria can decrease NF-kB activity and protect against NEC in an animal model. Probiotics are bacteria which have beneficial health effects beyond their inherent nutritive value. Recent clinical trials suggest that probiotics may confer some protection against NEC. This proposal is designed to 1. Assess possible mechanisms behind deficient down-regulation of NF-kB signaling via IkBa and A20 in immature IEC. 2. Determine the ability of secreted bacterial products from the probiotic organisms Lactobacillus plantarum, Lactobacillus acidophilus, and Bifidobacterium infantis to protect against necrotizing enterocolitis in an animal model without the introduction of live organisms. The experimental design uses two models of immature IEC - IEC isolated from pre-weaned mice and the human fetal small intestinal cell line H4. Both conventional and germ-free mice will be used. To model disease, the well established Caplan rat model of NEC will be used. This proposal will yield important information regarding aspects of intestinal immaturity which contribute to NEC and which are relevant to understanding the effect of any proposed treatment. Furthermore understanding the potential role of microbe free probiotic conditioned media may allow a means to administer the beneficial effects of probiotics without the risk of live organisms, thus providing a novel approach to treating or preventing NEC in at risk infants.